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Class 10 Science PYQ chapter wise: marks per chapter in the 2025 and 2026 board papers

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In short: we read two real CBSE Class 10 Science board papers question by question, set 31/1/1 of 2025 and set 31/2/1 of 2026, and counted the marks each NCERT chapter carried. Every chapter appeared in both papers, and in both the totals for each unit matched CBSE's official unit marks. The 2026 paper also had a new layout, split into Biology, Chemistry and Physics sections. Below are the counts, where to download the papers free from CBSE, how to use them chapter by chapter, and 8 questions of our own in the same styles, with worked answers.

The 8 practice questions are our own, drafted with AI help. Every answer was checked against the textbook pages named under it and re-computed by a test script, but no practising teacher has reviewed them yet. If you find a mistake, please tell us. We do not copy past-paper questions here; for those, use CBSE's own files linked below.

Where to get the official papers

CBSE puts its board question papers on the "Question Paper" page of cbse.gov.in, free, as one zip file per subject and year (Science is code 086). Each zip holds several sets, such as 31/1/1, 31/1/2 and 31/1/3. The sets of one year are different papers of the same design, so a chapter's marks can change a little from set to set. CBSE's "Marking Scheme" page has the step marks for the same papers.

How the two papers were laid out

Both papers have 39 questions for 80 marks. The 2025 paper (31/1/1) ran in five sections by question type: 20 one-mark questions (16 multiple choice and 4 assertion-reason), 6 two-mark, 7 three-mark, 3 five-mark and 3 four-mark case-based questions. The 2026 paper (31/2/1) was arranged by subject instead: a Biology section worth 30 marks, then Chemistry worth 25 and Physics worth 25, and students had to answer each section in its own part of the answer book. Each section mixed one-mark, short, long and case-based questions.

Marks per chapter in two real papers

NCERT chapter2025 (set 31/1/1)2026 (set 31/2/1)
1 Chemical Reactions and Equations46
2 Acids, Bases and Salts67
3 Metals and Non-metals106
4 Carbon and its Compounds56
5 Life Processes86
6 Control and Coordination47
7 How do Organisms Reproduce?116
8 Heredity26
9 Light, Reflection and Refraction116
10 Human Eye and the Colourful World16
11 Electricity87
12 Magnetic Effects of Electric Current56
13 Our Environment55
Total8080

By unit, both papers give Chemical Substances (Chapters 1 to 4) 25, World of Living (5 to 8) 25, Natural Phenomena (9 and 10) 12, Effects of Current (11 and 12) 13 and Natural Resources (13) 5: exactly the unit marks in CBSE's 2026-27 curriculum. So the units are fixed, but the split inside a unit moved a lot between the two years: Metals and Non-metals fell from 10 marks to 6, Heredity rose from 2 to 6, and The Human Eye rose from 1 to 6. The 2026 paper spread the marks much more evenly, with every chapter at 5 to 7.

Two calls we made. In 2025, question 30 (chromosomes, and how sexual reproduction keeps a species' DNA content stable) is counted under How do Organisms Reproduce?, and question 36 (the power of a lens, with the eye defect it corrects, and the refraction of light through a glass slab) under Light. Every other question, including both options of each internal choice, belongs to one chapter.

Where the big questions came from. The 5-mark questions were Carbon and its Compounds, How do Organisms Reproduce? and Light in 2025, and How do Organisms Reproduce?, Carbon and its Compounds and Magnetic Effects of Electric Current in 2026. The 4-mark case studies were salts, life processes and domestic electric circuits in 2025, and the brain, the chlor-alkali process and the heating effect of current in 2026.

How to use past papers chapter by chapter

  1. Finish the chapter first. Do the NCERT questions and our chapter guide before you open past questions on it.
  2. Sort by chapter, then by marks. List each chapter's past questions under it; you will see the same kinds come back, such as balancing and naming reactions, pH and salts, ray diagrams and the lens formula, resistances in series and parallel, and Mendel's crosses.
  3. Practise the 2026 layout. Since the 2026 paper is split into Biology, Chemistry and Physics, revise and time yourself by subject: 30 marks of Biology, 25 of Chemistry and 25 of Physics.
  4. Mark your own work against the marking scheme. CBSE publishes the marking schemes on its website; see where the step marks go, not only the final answer.
  5. Plan by unit. Chemical Substances and World of Living carry 50 of the 80 marks; our weightage guide has the full table.

8 PYQ-style questions, our own, with answers

Question 1 (1 mark, Metals and Non-metals). Non-metals are generally dull. Name the non-metal that the chapter gives as the exception that is lustrous.

Answer: iodine. The chapter lists it among the exceptions: although it is a non-metal, iodine shines. (Exceptions to the general properties, page 40.)

Question 2 (1 mark, Acids, Bases and Salts). Potassium hydroxide solution is added to dilute nitric acid until the mixture is neutral. Name the salt formed and the type of reaction.

Answer: potassium nitrate (KNO₃); a neutralisation reaction. KOH + HNO₃ → KNO₃ + H₂O: a base and an acid react to give a salt and water. (Neutralisation, page 21; potassium nitrate among the salts of Activity 2.14, page 29.)

Question 3 (2 marks, Electricity). A 60 W bulb and a 100 W bulb, both rated for 220 V, are joined in parallel to a 220 V supply. (a) What is the total power drawn? (b) Which bulb draws the larger current, and how large is it?

Answer: (a) 160 W; (b) the 100 W bulb, about 0.45 A. In parallel each bulb gets the full 220 V and works at its rated power, so the total is 60 + 100 = 160 W. From P = VI, I = P/V: 100 ÷ 220 ≈ 0.45 A for the 100 W bulb and 60 ÷ 220 ≈ 0.27 A for the 60 W bulb. (Electric power, P = VI, page 191.)

Question 4 (2 marks, Light). An object is placed exactly at the principal focus of a convex lens. Where is the image formed, and what is it like?

Answer: at infinity; it is real, inverted and highly enlarged (infinitely large). Rays from a point at the focus leave the lens parallel to one another, so they meet only at infinity. (Image formation by a convex lens, the table on page 152.)

Question 5 (3 marks, Life Processes). Trace the path of the oxygen in a breath of air from the nostrils to a muscle cell in the leg.

Answer: Air enters through the nostrils and passes down the air passages into the lungs, which end in tiny balloon-like alveoli (pages 89 and 90). In the alveoli oxygen passes into the blood in the thin blood vessels of their walls, where haemoglobin in the red blood corpuscles takes it up (page 90). This oxygen-rich blood returns to the heart, entering the left atrium, then the left ventricle, which pumps it out to the body (page 92). Through the arteries and then the thin capillaries, the oxygen reaches the muscle cells, which use it in respiration.

Question 6 (3 marks, Heredity). In a plant, red flower colour (R) is dominant over white (r). A plant with red flowers of genotype Rr is crossed with a white-flowered plant (rr). (a) What gametes does each parent make? (b) What fraction of the offspring will have red flowers? (c) Why can no offspring be RR?

Answer: (a) Rr makes R and r gametes in equal numbers; rr makes only r. (b) One half: Rr and rr offspring come in a 1 : 1 ratio, so half are red (Rr) and half white (rr). (c) The white parent gives only r, so every offspring gets at least one r. Each parent passes on one copy of the gene, and the dominant trait shows whenever R is present. (Mendel's rules of inheritance, dominant and recessive traits, pages 129 to 131.)

Question 7 (5 marks, Electricity). A microwave oven rated 1,200 W on 220 V is used for 30 minutes every day for 30 days. Electricity costs ₹8 a unit (kW h). Find (a) the energy used in kW h, (b) the cost, (c) the current it draws, (d) the resistance of the oven at its rating, and (e) whether a 5 A fuse would suit it, and why.

Answer: (a) 18 kW h; (b) ₹144; (c) about 5.45 A; (d) about 40.3 Ω; (e) no. (a) Energy = power × time = 1.2 kW × 0.5 h × 30 = 18 kW h. (b) 18 × ₹8 = ₹144. (c) I = P/V = 1200 ÷ 220 ≈ 5.45 A. (d) R = V²/P = 220² ÷ 1200 = 48,400 ÷ 1200 ≈ 40.3 Ω. (e) The normal current, about 5.45 A, is more than 5 A, so a 5 A fuse would melt every time the oven ran; the next rating up, 10 A, would suit it. (Power and energy, pages 191 and 192; the fuse and its ratings, page 190.)

Question 8 (4 marks, case-based, How do Organisms Reproduce?). A bee picks up pollen from a mustard flower in one field and then visits a mustard flower on a different plant, where some of the pollen sticks to the stigma. (a) Is this self-pollination or cross-pollination? (b) How does the male germ-cell then reach the ovary? (c) After fertilisation, what do the ovule and the ovary become?

Answer: (a) cross-pollination; (b) through a pollen tube; (c) the ovule becomes a seed and the ovary a fruit. (a) The pollen moved from one flower to another, which is cross-pollination; transfer within the same flower is self-pollination. (b) The pollen grain grows a tube, which passes down through the style until it reaches the ovary. (c) The zygote forms an embryo inside the ovule, which develops a tough coat and becomes a seed, while the ovary grows and ripens into a fruit. (Sexual reproduction in flowering plants, page 121.)

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Sources

All opened and read on 4 November 2026. Page numbers are the printed page numbers of the textbook.

The chapter counts are our own reading of the two CBSE papers named above; we have not reproduced any question from them. The 8 practice questions and worked answers are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the official CBSE notices.

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